1. Field of the Invention
The present invention concerns the valuable use made of liquid and/or solid waste of different kinds coming from different sources. It relates more especially to the treatment both in an external atmosphere (aerobic phase) and in a closed medium (anaerobic phase) of organic waste and polluted materials, respectively solid or semi-solid and liquid, for directly and simultaneously producing compost, biogas and purified liquid.
2. Description of the Prior Art
The increasing volume of waste and residues of all types constitutes an increasing problem for industrialists and municipalities, considering more especially the fact that this waste generally presents great dangers for the environment and for living beings.
Very often, for liquid residues, the solution is adopted of solidifying this waste by a physico-chemical treatment giving rise to petrifaction, the hard masses obtained remaining on the treatment site or being possibly used for constructing foundation structures or different ground coverings.
According to another objective, attempts are made to make valuable use of a part at least of this waste, for example by producing heat energy or, better still, when it is a question of organic residues more or less rich in carbon and other non mineral substances, by using the known techniques of fermentation in an aerobic and/or anaerobic medium so as to obtain either composts, fertilizers and different improvements to soils or production of a gas called "biogas" rich in methane and usable as a fuel for obtaining heat or electric energy or else for manufacturing chemical products.
The invention relates to this field of making valuable use of organic waste and has essentially as aim, at one and the same time, of transforming solid organic waste into useful materials, particularly for agriculture and ensuring the treatment of liquid organic waste so as to depollute it and obtain, on the one hand, biogas and on the other purified fluids directly usable for industry or consumption.
Among the solid waste or sub-products usable as raw material in the invention, the following in particular may be mentioned: screened fractions of household waste, straw, sawdust and wood bark and ligneous materials, grape pulp, draff, bagasse, peat, herbaceous plants . . . etc.
As for liquid residues, they may in particular comprise all the concentrated refuse coming from agricultural and agricultural food production industries such for example as: sugar refineries, wine distilleries, breweries and fermentation industries, slaughter houses, and meat canning works, the dairying industries, potatostarch works, pig breeding installations . . . etc. as well of course as all the excess primary sludge and biological sludge recovered in stations for purifying urban waste water.
In what follows, the term semi-solid waste or residues will be used for designating normally solid materials but which have a water content generally between 30% and 90%, for example of the order of 45 to 80% approximately.
Fermentation in a heap, so in an aerobic medium, of different solid agricultural residues is already known for producing compost. However, these are long operations which do not in general lend themselves very well to industrialization. Moreover, producing biogas by anaerobic fermentation of semi-solid residues or sludges in digesters is known. However, this apparatus must be usually heated so as to obtain correct efficiency and the mass to be treated must be agitated and stirred; furthermore, the concentration of sludge must be made in decanters, for example lamellar decanters separate from the digester.
The essential aim of the invention is to propose a process associating the two types of aerobic and anaerobic fermentation so as to be able to simultaneously treat solid or semi-solid waste and liquid waste in order to obtain, at the outlet of a single installation, the production: of solid materials rich in fertilizing substances, biogas usable as a fuel or similar, and finally purified liquids which are immediately reusable and admissible by the environment.
Another aim is to use the heat from the aerobic fermentation so as to provide, without the need for an external supply, the ideal heat balance for the anaerobic digestion of the liquid waste or residues.
A further aim is to provide a type of digester requiring no mechanical stirring member and in which the stirring of sludge material is provided by the pressure alone of the gas generated by the fermentation in a closed medium.
Finally, yet other aims will appear from the following description, particularly the use of micro-organisms and/or enzymes, preferably fixed on certain supports, with the aim of accelerating the biological transformation process and increasing the production yields in industrial units.